Refractory metals and their suicides are widely used in CMOS DRAMs and logic circuits. Silicides offer lower resistivity compared to doped silicon. In addition, silicides also offer higher thermal stability compared to conventional interconnect materials such as aluminum. There are several ways to obtain refractory metal silicide films on the wafer. The most common method to obtain metal silicide is through the salicide process. The salicide process for obtaining titanium silicide film on a wafer is described below:
1. a layer of Ti is deposited on a wafer by sputtering; PA1 2. first rapid thermal anneal (RTA) step: titanium reacts with silicon forming TiS.sub.2 ((C49) phase). This step is done in a nitrogen atmosphere to avoid forming TiSi.sub.2 on the oxide and forms a TiN layer on the titanium; PA1 3. the wafer is removed and selectively etched to the TiN and unreacted Ti; PA1 1. eliminates the need for high temperature rapid thermal annealing steps, provided a C54 film can be deposited; PA1 2. reduces silicon consumption from the wafer; PA1 3. eliminates the phase transformation step; and PA1 4. provides an opportunity to deposit an amorphous film.
a. a second RTA step is performed whereby TiSi.sub.2 is transformed from the high resistivity phase (C49) to the low resistivity phase (C54).
The process involves four steps including two high temperature rapid annealing steps. The advantage of RTA versus conventional annealing is that RTA reduces the "thermal budget", defined as the time the wafer stays in the furnace at high temperature. In general, reducing the thermal budget is desirable.
An alternative way to obtain a silicide film on a wafer would be by depositing a suilcide film by sputtering a silicide target. Sputter deposition of silicide film using a silicide target offers the following advantages:
Aluminides of Ti and Ta are useful barrier materials in the manufacture of integrated circuits. During the manufacture of integrated circuits Ti and Al layers often react to form titanium aluminide during wafer processing. However, formation of titanium aluminide during wafer processing is detrimental to the wafer because it introduces additional stresses in the film and also consumes Ti and Al from interconnect wiring. In order to prevent titanium aluminide formation and consumption of interconnect metal in the wafer during processing, it is desirable to deposit titanium aluminide by sputtering a titanium aluminide target Depositing a titanium aluminide film eliminates the introduction of stresses associated with formation of titanium aluminide and unnecessary consumption of interconnect metal.